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<div class="document" id="xapian-java-bindings">
<h1 class="title">Xapian Java Bindings</h1>

<p>The current API should be regarded as experimental - we plan to review it,
possibly make some changes and then declare it stable early in the 1.4.x
release series.</p>
<div class="section" id="how-to-build-the-bindings">
<h1>How to build the bindings:</h1>
<p>If you want to install from source you'll need to <a class="reference external" href="https://xapian.org/download">download the source
code</a> if you haven't already done so.</p>
<p>Running &quot;make&quot; and then &quot;make install&quot; will &quot;install&quot; a JNI glue shared library
into a &quot;built&quot; subdirectory of the java build directory.  The jar file is built
into the &quot;built&quot; subdirectory too.</p>
<p>You can copy these two files into your java installation, or just use them
in-place.</p>
</div>
<div class="section" id="how-to-compile-the-examples">
<h1>How to compile the examples:</h1>
<pre class="literal-block">
cd java
javac -classpath built/xapian.jar:. docs/examples/SimpleIndex.java
javac -classpath built/xapian.jar:. docs/examples/SimpleSearch.java
</pre>
</div>
<div class="section" id="how-to-run-the-examples">
<h1>How to run the examples:</h1>
<p>To run the examples, you need to give Java a special system-property named
&quot;java.library.path&quot;.  The value of this property is the path of the directory
where the libxapian_jni.so (or whatever extension is used on your platform)
JNI library is located.</p>
<pre class="literal-block">
java -Djava.library.path=built -classpath built/xapian.jar:docs/examples \
     SimpleIndex ./test.db index words like java

java -Djava.library.path=built -classpath built/xapian.jar:docs/examples \
     SimpleSearch ./test.db index words like java
</pre>
<p>Alternatively, you can avoid needing the <cite>-Djava.library.path</cite> setting by
setting the <cite>LD_LIBRARY_PATH</cite> environment variable, or by installing the JNI
library in the appropriate directory so your JVM finds it automatically
(for example, on macOS you can copy it into <cite>/Library/Java/Extensions/</cite>
- you can also copy the <cite>.jar</cite> file there and avoid needing to specify it
via <cite>-classpath</cite>).</p>
<p>The java bindings have been tested recently with OpenJDK versions 1.8.0_77,
1.7.0_03, and 1.6.0_38, but they should work with any java toolchain with
suitable JNI support - please report success stories or any problems to the
development mailing list: <a class="reference external" href="mailto:xapian-devel&#64;lists.xapian.org">xapian-devel&#64;lists.xapian.org</a></p>
</div>
<div class="section" id="strings-and-binary-data">
<h1>Strings and binary data</h1>
<p>The Xapian C++ API is largely agnostic about character encoding, and uses
the <cite>std::string</cite> type as an opaque container for a sequence of bytes.
In places where the bytes represent text (for example, in the
<cite>Stem</cite>, <cite>QueryParser</cite> and <cite>TermGenerator</cite> classes), UTF-8 encoding is used.
In Java, the <cite>String</cite> class uses UTF-16 encoding, and can't hold arbitrary
binary data.</p>
<p>The approach taken to this problem by these bindings (in Xapian 1.4.4 and
later) is to map C++ <cite>std::string</cite> to/from Java byte arrays (<cite>byte[]</cite>) in
places where the data is inherently binary (serialisation functions) or likely
to be binary (document values).</p>
<p>This loses a bit of generality compared to the C++ API - for example, in C++
you can add a term with a binary data value but in Java it has to be a
Unicode string.  But users rarely actually need or want that generality,
and losing it means that you can just work with Java <cite>String</cite>.</p>
<p>Document values work best when the values are compactly encoded, so a binary
encoding is usually appropriate.  However, if you really want to put a text
value in a document value slot you can explicitly convert <cite>String</cite> to/from
a byte array of UTF-8 data like so:</p>
<pre class="literal-block">
import java.nio.charset.StandardCharsets;

//...

doc.addValue(1, some_string.getBytes(StandardCharsets.UTF_8));

//...
String value = new String(doc.getValue(1), StandardCharsets.UTF_8);
</pre>
<p>As well as terms, document data and user metadata are also required to be
text at the moment when using these bindings.</p>
</div>
<div class="section" id="naming-of-wrapped-methods">
<h1>Naming of wrapped methods:</h1>
<p>Methods are renamed to match Java's naming conventions.  So get_mset becomes
getMSet, etc.  Also get_description is wrapped as toString.</p>
</div>
<div class="section" id="matchall-and-matchnothing">
<h1>MatchAll and MatchNothing</h1>
<p>In Xapian 1.3.0 and later, these are wrapped as static constants
<tt class="docutils literal">Query.MatchAll</tt> and <tt class="docutils literal">Query.MatchNothing</tt>.</p>
<p>If you want to be compatible with earlier versions, you can continue to use
<tt class="docutils literal">new <span class="pre">Query(&quot;&quot;)</span></tt> instead of <tt class="docutils literal">Query.MatchAll</tt> and <tt class="docutils literal">new Query()</tt> instead of
<tt class="docutils literal">Query.MatchNothing</tt>.</p>
</div>
<div class="section" id="todo-list">
<h1>TODO list:</h1>
<ul>
<li><p class="first">Write SimpleExpand.java.</p>
</li>
<li><p class="first">Fix string passing to be zero-byte clean:
<a class="reference external" href="https://trac.xapian.org/ticket/46">https://trac.xapian.org/ticket/46</a></p>
</li>
<li><p class="first">These were missing in the JNI bindings - it would be good to add them to
SmokeTest.java:</p>
<blockquote>
<ul class="simple">
<li>optional parameter &quot;parameter&quot; for Query ctor.</li>
<li>new QueryParser API.</li>
<li>changes to Enquire sorting API.</li>
<li>new method ESet::back().</li>
<li>Third (optional) argument to Document::add_posting().</li>
<li>Xapian::Weight and standard subclasses.</li>
</ul>
</blockquote>
</li>
</ul>
</div>
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